How do i remove the the default HDRI in Blender 2.8 eevee?
There shouldn't be any HDRI applied when creating a new project. You can set your own HDRI or change an existing one in the world tab. If you want to remove an existing HDRI you delete the nodes connected to the color socket or change the texture to one you like better.



Click on the button behind the color field.



Select environment texture from the dropdown. This will allow you to select an image that is used as background.



Click on Vector and select the Mapping node. This allows you to change the orientation of the HDRI.



Click on the Vector socket of the Mapping node and select Generated from the dropdown. You select and .hdr or .exr image to light your scene

 

Example of how it could look like.